Fiber-reinforced plastic, which is also known as fiber-reinforced polymer, and most generally as composite material, is made of a polymer matrix that is reinforced with fibers that are characterized by high strength and stiffness. The fibers are usually made from glass, carbon, quartz, basalt or aramid, although other fibers such as cellulose and asbestos are sometimes used. The polymer matrix is usually a thermosetting-type plastic such as epoxy, vinylester, bismaleimide, polyimide, phenolic, or polyester but other resins are also used. The fiber reinforcement can be present in various forms including continuous fibers, chopped fibers, woven fabrics, braided fabrics, or other forms. Fiber composites, especially those of the strongest and most rigid fiber, such as carbon fiber, can exhibit a significantly higher strength to weight ratio in comparison to metals, resulting in a potential weight savings of up to about 50 percent. Composite materials are commonly used in the aerospace, automotive, marine, and construction industries. Generally speaking, fiber composites have superior fatigue properties in comparison to metallic structures and are corrosion resistant. With such advantageous structural properties, fiber composites are most suitable for use in aircraft components.
Fiber composite materials are made by first creating bundles of fibers called tows or yarns that typically contain thousands of individual fibers. The fiber tows that are then dipped in polymer resin to produce a “towpreg” in which the resin is impregnated between the individual fibers in the tow. Alternatively, fiber tows can be combined side by side to form a sheet of fibers which are then dipped in a polymer resin or coated with a polymer resin to produce a “prepreg”. The towpreg or prepreg material is then stacked in layers by processes such as filament winding, hand layup, and tape laying and cured by means of cross-linking of polymer chains by means of catalysts, heat, and/or radiation to form a rigid composite structure. An alternative process first forms the fiber tows into a “preform” fabric by weaving or braiding. The dry fabric can then be coated with a resin to form a woven or braided prepreg, or the thy fabric can be placed into a mold followed by infusion of the resin into the mold and curing of the composite within the mold.
One major difficulty in the use of fabricated fiber composite engineered products is that, during use when repeated stresses are applied to the final products, high local stresses develop within individual tows and between tows causing cracking within the fiber tows and delamination between tows that can lead to parts failure. There are methods by which to reduce the potential for such internal failure processes, such as by various modifications of and additions to the resin matrix material, so as to strengthen it. More generally speaking, toughening and other property enhancements of composite materials are typically implemented by modifying the bulk properties of the constituents, either the fiber or matrix materials, though this often leads to difficulties in processing and thus to higher costs.
Investigations of the failure and damage mechanisms of textile composites has led to the conclusion that toughening of the matrix material would result in increased material performance. In this regard, several methods have been used in which the bulk of the matrix is modified either through chemical formulation or the addition of fillers. However, such methods can detrimentally affect the processability of the resulting matrix material. Other methods exist that rely on modification of the fiber material (so-called “fuzzy fiber” approaches) that can also result in reduced fiber performance.
Attempts have been made to overcome the processing challenges associated with fiber composite production while improving the fiber's structural properties according to the final use of various composite structures. But there still exists a need for more efficient methods of enhancing or improving the structural properties of carbon and other fibers.